<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <button>删除</button>
    <ul>
        <li></li>
        <li></li>
        <li></li>
        <li></li>
        <li></li>
    </ul>
    <script>
        var button = document.querySelector('button');
        var ul = document.querySelector('ul');
        button.onclick = function() {
            if (ul.children.length !== 0) {
                ul.removeChild(ul.children[0]);
            } else {
                button.disabled = 'true';
            }
        }
    </script>
</body>

</html>